Knock three times and experience 3- 1=2 time intervals, from which we can find that 1 time interval is 6÷2=3 seconds, then knock nine times and experience 9- 1=8 time intervals, and multiply by 3.
Solution: 6(3- 1)×(9- 1)
=6÷2×8
=24 (seconds)
A: It takes 24 seconds to knock 9 times.
Similar mathematical problems and their solutions
1, the problem of climbing the building: 1 The middle of the building climbing to the fourth floor is 4- 1=3 intervals. If we have time to climb from the first floor to the fourth floor, we can know how long it will take to climb the first floor. Then when you get the final answer, multiply the time of one floor by the total number of floors climbed.
2. Clock pointer problem: 1 goes to 7 o'clock, with 7- 1=6 intervals in the middle. If you know the time to go to 7 o'clock, you can calculate the time of each interval. We can calculate the total time required for the result by multiplying the time of each interval by the total interval.